Deburring and like surface treatments utilizing a blast medium, e.g. granules, pellets or other particles of an abrasive or relatively hard substance, or the removal of lacquer and other coatings from articles by a blast medium are techniques which are commonly in use in industry.
For the deburring of rubber or synthetic resin (plastic) material or the comminution thereof or parts thereof, it is advantageous to subject the articles to a preliminary embrittlement treatment, e.g. by deep-cooling them.
The same applies for the embrittlement of lacquer and like coatings of materials which can be more easily removed from workpieces after the latter have been embrittled by deep-cooling. The deep-cooling process can utilize direct heat exchange between the articles and a deep-cooling medium, e.g. a liquefied gas such as liquid nitrogen.
In the past, the deburring technique and/or the surface treatment for coating removal has been effected in a rotary drum, a trough-shaped receptacle in which the articles are given a movement or are radially displaced relative to one another, or even on a rotary inclined table in which the articles can be moved about so that practically all surfaces therein can come into contact with the blast medium. Generally, the blast medium is, as has been noted, a stream of particles which are directed toward or at the workpieces utilizing the centrifugal action of a rotor, e.g. a blast rotor or, as more accurately defined, a sling wheel or rotor which flings the particles at a high velocity by virtue of centrifugal force against the workpieces.
With comparatively large articles to be deburred and/or to be surface-treated with a blast medium, e.g. respirator masks, and other large or bulky articles, problems are encountered with such treatments since the movement of the article to expose all of the surfaces to the blast, particularly when the articles are highly embrittled, may result in undesired breakage.
Without such movement, however, the article may be incompletely deburred or insufficiently treated so that portions of a coating may remain.
The prior-art apparatuses for such surface treatments, especially where the articles were subjected to low temperature treatments prior to the surface treatment, generally operated unsuccessfully.
Of course, other apparatus for the deburring or coating removal of articles are operated with transport systems, e.g. conveyors, which carry the articles through a transport zone or along a transport path extending through the blast zone.
In such arrangements, two or more sling wheels had to be disposed above one another in a common vertical plane or otherwise ganged to ensure full coverage of the workpieces. In a large measure, the drawbacks of these earlier systems were due to the inability to deliver large quantities of the blast medium to the or each sling wheel and/or problems encountered by the requirements for journaling the sling wheel in the region in which the articles were to be subjected to the treatment.